Pulp screening machine



Feb. 4, 1941. N, m HT a, 2,230,647

PULP SCREENING MACHINE Filed July 9, 1938 4 Sheets-Sheet l Fig.1.

4| eson M.Kni hT 40 5 b 'WSZ-JMMW 'lnvenTon'f Feb. 4, 1941- v N, KNIGHT 2,230,547

PULP SCREENING MACHINE Filed July 9, 1958 4 Sheets-Sheet 2 Fig.2.

lnvenTor.

Nlson M. Kn ighr V bymdwiw ATTys,

Feb. 4, 1941. N KNlGHT 2,230,647

PULP SCREENING MACHINE Filed July 9, 1938 4 Sfieets-Sheet 3 lnvenToF.

Nelson M. Knighr b MMx W A i TyS.

Feb. 4, l I 1. N. M. KNIGHT PULP SCREENING MACHINE Filed July 9, 1938 4 Sheets-Sheet 4 lnvegwror. Ne \so,n M.KnighT ATTys.

Patented Feb. 4, 1941 UNITED STATES PATENT OFF-ICE PULP SCREENING MACHINE Nelson M. Knight, Boston, Mass.

Application July 9, 1938, Serial No. 218,381

4 Claims.

This invention relates to pulp screening machines which have a casing provided witha pulp inlet and a screened pulp outlet, and a screen within the casing between the inlet and the outlet for the purpose of screening the pulp,

In the operation of pulp screens, the coarse material and tailings which cannot pass through the screen gradually accumulate on the inlet side thereof, and if allowed to remain would seriously interfere with the screening operation.

It is customary to provide pulp screening machines with some form of screen-cleaning device having for its purpose to remove the coarse or waste material from the screen as it accumulates thereon, and it is one of the objects of my present invention to provide an improved form of screen-cleaning device which is movable over the screen and which is so constructed that as it moves over the screen, sufllcient suction is produced by its movement at its trailing side to withdraw by suction all coarse or waste material from the screen.

I have herein shown my invention as embodied in a pulp-screening machine of the type shown in my Patents No. 2,003,150 dated May 23, 1935,

and No. 2,122,475, dated July 5, 1938. This type of pulp screen has a cylindrical screening element situated within the casing and the screencleaning member encircles the screen and rotates thereabout and is provided with blades or runners that move over the outer surface of the screen. In adapting my invention to this type of pulp-screening machine, I make the blades of the screen-cleaning element of such cross-sectional shape that during rotation around the screen, a vacuum condition will be established at the trailing side of the blade and close to the screen, the result of which will be that the suetion thus produced pulls all the waste or coarse material from the face of the screen, leaving the screen clean for further screening operation.

Another feature of my invention relates to a novel construction involving a series of baiile plates secured to the casing and between the latter and the screen-cleaning member and which have for their purpose to compel the pulp to be force-.1 back and forth through the screen a plurality of times during its passage from the inlet to the outlet and to prevent establishment of a flow of unscreened pulp along the inner wall of the casing from the inlet to the tailings outlet.

In order to give an understanding of my invention I have illustrated in the drawings a selected embodiment thereof which will now bedescribed-after which the novel features will be pointed out in theappended claims.

In the drawings:

Fig. 1 is a vertical sectional view through a pulp-screening machine embodying my inven- 5 tion; I

Fig. 2 is an enlarged horizontal section on the line 22, Fig. 1;

Fig. 3 is a fragmentary sectional view showing one of the blades of the screen cleaning element 10 and illustrating the manner in which it operates to clean the screen by suction;

Fig. 4 is a side view of one section of the screen-cleaning element.

Figs. 5 and 6 are fragmentary sectional views 15 illustrating the relative movement of the pulsating plates and the baille plates;

Fig. 7 is a graph illustrating the relative movements of the pulsating plates and battle plates.

Inthe drawings, I indicates generally the cas- 20 ing of the-pulp-screening machine, this being shown as a vertical cylindrical casing having an upper head 2 provided with an inlet 3 for the pulp to be screened and also having a lower head 4 provided with a central outlet 5 for the dis- 25 charge. of screened pulp. The casing is shown as supported on suitable legs or supports 6, and the upper head 2 has attached thereto a fitting or hearing member I having an inlet passage 8 through which the unscreened pulp is delivered 30 to the inlet 3,

The casing l herein illustrated is constructed similarly to that shown in my Patent No. 2,122,475, and it comprises a plurality of curved plates 9 which are connected by bolts ill to verti- 35 cally extending posts H. i

The screen which is situated within the casing l is indicated at l2 and is shown as a cylindrical screen. Said screen is connected at its upper end to a screen head l3 and at its lower end 4 to another screen head It, the head l4 being provided with the central outlet opening l5 which communicates with the discharge opening 5 and through which the screened pulp flows.

The unscreened pulp thus flows into the casing 45 from the baflle plates thereby causing the pulp to be pulsated or forced back and forth through the screen l2 as it flows from the inlet to the outlet. The general construction of these bame plates and pulsating plates is the same as that disclosed in my above mentioned patents. The baflle plates are held spaced relative to each other by suitable spacers H! which are tied together by the tie rods 26, and which extend through openings 13 in the pulsating plates l8. The pulsating plates l8 are carried by a spindle 2| situated axially of the screen and which is vibrated in the direction of its axis. This spindle 2| is provided with a plurality of radially extending arms 22 to which certain of the pulsating plates are secured and the other pulsating plates are tied to those pulsating plates which are secured to the radiating arms 22 by means of tie rods 23. The pulsating plates are held spaced from each other by spacers 26 which pass through openings 25 in the baiiie plates in the manner described in my above mentioned Patent 2,122,475.

The vertical vibration of the spindle 2i is derived from an eccentric portion 26 of a drive shaft which has a driving pulley 21 fast thereon, the latter being driven by a. belt 28 from a suitable motor 29. The eccentric 26 has an eccentric strap 30 which is connected to the upper end of the spindle 2| as shown at 3|, so that rotation of the driving shaft causes an up-and-down vibratory movement of the spindle.

As stated above the screen i2 is yieldingly supported. The yielding support therefore is somewhat similar tothat illustrated in my said Patent No. 2,122,475, and comprises a plurality of rubber balls 32 which are confined between lower seat members 33 supported by the lower casing head 4 and upper seat members 33 which rest against or are secured to the lower screen head it.

During the downward movement of the pulsating plates, each pulsating plate moves toward the bafile plate directly beneath it with the result that the pulp between any two plates that are appreaching each other will be forced outwardly through the screen and at the same time pulp will flow inwardly through the screen into the enlarging space between each pulsating plate and baflie plate directly above it. This downward movement of the pulsating plate produces a downward pressure .on the baflle plates and thus on the screen which causes the yielding balls 32 to be compressed slightly and thus permits a slight downward movement of the screen.

In the device herein illustrated there is provided. an additional set of rubber balls 35 which are situated below the lower casing head 3 and are connected to the screen so that during the upward movement of the pulsating plates the upward pressure produced on the baflle plates'and screen will serve to compress the balls 35 as the balls 32 were compressed during the downward movement of the pulsating plates.

These rubber balls 35 are confined between upper seat members 35 which rest against the underside of the lower casing head 4 and lower seat members 31. The tie rods 23 extend from the upper screen head l3 through the spacers is, through the lower screen head l4, the balls 32 and their seats 34, 33, and through the lower casing head 4, the additional set of balls 35 and their seats 36, 31. The tie rods 20 are provided at their lower ends with suitable clamping nuts 38 by which the lower seat members 31 are tied to the screen structure.

With the construction above described including the two sets of rubber balls 32 and 35, the

screen will have an upward and downward movement during each upward movement of the pulsating plates, and will have both a downward and an upward movement during ,each downward movement of the pulsating plates. This is illustrated in Figs. 5, 6 and 7, Figs. and 6 being somewhat in the nature of diagrammatic views whichshow a portion of the screen l2 with its baflie plates "5 and also some of the pulsating plates i8.

Since the spindle 2| is operated by an eccentric said spindle will have a simple harmonic motion, and during each half rotation of the eccentric which moves the spindle from one end to the other of its stroke, the velocity of the spindle will increase progressively from zero to its maximum speed during the first quarter of the revolution and will decrease progressively from maximum to zero during the second quarter of the revolution, the spindle being at rest for an instant while the eccentric is passing either its high point or its low point.

Assuming that the spindle 2| is at its.low point and that the pulsating plates and bame plates have the relative position shown in Fig. 5, then during the first quarter revolution, the pulsating plates will be moved upwardly from the full line position, Fig. 5, to the dotted line position, and during this movement, the pressure to which the pulp above the pulsating plates is subjected by the upward movement thereof will partially be transferred to the baiiie plates it thus causing the baiiie plates and screen to be raised slightly as shown by the dotted lines in Fig. 5. The maximum pressure which is generated by the upward movement of the pulsating plates occurs when the pulsating plates have reached their maximum speed in an upward direction, and this occurs at the end of the first 90 movement oi! the eccentric. This upward movement of the screen will serve to compress the rubber balls 35. During the second 90 movement of the eccentrlc which carries the spindle to the upper limit of its stroke and which moves the pulsating plates 58 from the dotted line position Figs. 5 and 6 to the full line position, Fig. 6, the speed of movement of the pulsating plates is gradually diminishing from maximum to zero and, therefore, the pressure of the pulsating plates against the pulp directly above them will be gradually diminishing pressure. The rubber balls 35 thus receive their maximum compression at the end of the first 90 movement of the eccentric or when the pulsating plates l8 and baflie, plates i8 are in the dotted line position, Fig. 5. During the second 90 movement when the pressure of the pulp against the baiiie plates is a decreasing pressure and the pulsating plates are moving from the dotted line position to the full line position, 6, the balls 35 recover their original shape thus bringing the screen |2 back to its normal position, that is the full line position in Fig. 5. During this time, the baiiie plates will have a downward movement from the dotted line position back to the full line position and thus during the first half rotation of the eccentric and dining the resultant upward'movement of the pulsating plates from their low position to their high position, the bafile plates I6 and the screen |2 will have a slight upward movement and then a slight downward movement, thus practically subjecting the pulp to two pulsations.

The same operation occurs during the downward movement of the spindle 2| from its high point to its low point. During the first quarter of the downward movement, the pulsating plates |8 will move from the full to the dotted line position Fig. 6, and during this movement the speed or velocity of the pulsating plates is gradually increasing due to the simple harmonic. motion. The pressure developed on the pulp beneath the pulsating plates will force the bafile plates downwardly from the full line position Figs. 5 and 6 into the dotted line position Fig. 6. During the second 90 downward movement of the pulsating plates by which they are brought to the full line position, Fig. 5, from the dotted line positions Figs. 5 and 6, the speed of downward move ment of the plates is gradually decreasing and the pressure which the plates apply to the pulp beneath them is also a decreasing pressure. When the pulsating plates l8 have reached the dotted line position, Fig. 6, and the bafile plates l6 have been forced downwardly into the dotted line position, Fig. 6, the balls 32 will be compressed to their maximum extent and during the second 90 downward movement of the pulsating plates the balls 32 will recover thus moving the baille plates and screen upwardly from the dotted line position, Fig. 6, into the normal full line position shown in Figs. 5 and 6.

This relative movement of the screen and the baffle plates is illustrated graphically in Fig. 7 wherein the line m indicates the up and down movement of the pulsating plates and the line 11.

indicates the up and down movement of the baffle plates and screen. A comparison of the lines m and n show that the bailie plates and screen have an up and down movement during each up or down movement of the pulsating plates.

The use of the two sets of rubber balls 32 and 35 thus produce a double pulsating action between the pulsating plates and the baflie plates which is extremely effective in forcing the pulp back and forth through the screen and which, therefore, increases the screening effect.

The lower screen head I4 is provided with a depending sleeve portion 39 which extends into the opening 5 of the lower casing head 4, and this sleeve portion 39 is formed with radially extending arms 40 which support a guiding sleeve 4| through which the lower end of the spindle 2| extends. 42 is a spring which encircles the lower end of the spindle 2| and is confined between the guiding sleeve 4| and a collar 43 on the spindle, said spring serving to yieldingly support the weight of the spindle and pulsating plates while permitting the spindle to vibrate relative to the screen.

During the screening operation the coarse material which cannot pass through the screen will tend to accumulate on the outside thereof, and as in my Patent No. 2,003,150, and also in'my Patent No. 2,122,475, there is provided a screen-cleaning element which encircles the screen and rotates thereabout. In the present invention, however, this screen-cleaning element is constructed to clean the coarse unscreenable matter from the outside of the screen by suction.

The rotary screen-cleaning element is indicated generally at 44 and it comprises an upper head 45 above the screen and a lower ring member 46 below the screen, said head and ring being connected by screen-cleaning sections indicated at 41 and one of which is illustrated in Fig. 4.

The upper head 45 has a tubular neck 48 rising therefrom through which the spindle 2| extends, said neck extending through the bearing member 1 and having a collar 49 at its upper end which is rotatably supported on a suitable bearing member 50. The rotation is given to the screen-cleaning element 45 through a worm gear 5| which is secured to the head 49 and is driven by a worm 52 on a shaft 53 which has a sprocket wheel 54 thereon that is connected to a sprocket wheel 55 on the main driving shaft by means of a sprocket chain 56.

The screen-cleaning element 44 is thus rotated about the screen during the pulp-screening operations.

Each section 41 of the screen-cleaning element comprises an upper header 51 and a lower header 58 which are connected by vertical bars or runners 59. The upper header 51 is connected to the upper head 45 by suitable bolts 60 and the lower header .58 is connected to the ring 46 by suitable bolts 6|.

The cross-sectional shape of the blades or runners 59 is such that as these blades move around the screen l2 a strong suction action is produced on the trailing side of each blade which suction action is suflicient to suck or draw the refuse matter or tailings from the screen, thus leaving the screen clean for further cleaning operations.

While the blades may have various cross-sectional shapes which will accomplish this purpose, I have found the shape illustrated in Figs. 2 and 3 to be eminently satisfactory. Each blade is shaped to provide the convexly curved outer or leading side 62 and a trailing side formed with a concavely curved surface 63 adjacent the inner edge of the blade, that is, adjacent the edge nearest to the screen l2, which concavely curved surface merges into the convex surface 64 at the outer portion of the blade. The blade is preferably made with a relatively sharp inner edge 65 adjacent the screen.

Each blade has a slightly inclined position relative to a radial line as best seen in Figs. 2 and 3 and as the blades move through the pulp relative to the screen l2 in the direction of the arrows in Figs. 2 and 3, the leading side 62 of each blade forms a stream-line surface over which the pulp will flow with relatively small resistance. A greatly reduced pressure or a vacuum condition will be established, however, at the point immediately behind the concave surface 63 and the vacuum thus created at this point is suificient to suck the refuse matter from the outside of the screen and to leave the latter clean.

This action is illustrated somewhat diagrammatically in Fig. 3 wherein the coarse matter which accumulates on the outside of the screen is shown at 66. The screen blades 59 are supported with their inner edges 65 slightly spaced from the screen and if the layer of waste matter 66 on the screen in front of any blade is of considerable thickness, then the edge 65 will act as a plow to scrape off the outside portion of the layer 66. A considerable portion of the refuse matter, however, will pass between the edge 65 of the screen blade and the screen I! and any refuse which passes beneath the blade is drawn away from the screen by the suction created at 85 as shownby the shaded portion 61 in Fig. 3. By means of this suction the screen immediately back of each blade will be thoroughly cleaned and freed from any matter which cannot pass through the screen, and such coarse matter will flow over the stream-line portion 64 of the blade.

Each section 41 of the screen-cleaning member may have a plurality of these blades 59 and as each blade passes over any portion of the screen l2, it leaves such portion of the screen perfectly free from refuse matter.

- partitions 68 which connect the blades 59, and I have also shown the walls of the casing i as having rigid therewith annular baflle plates or rings 89 which extend inwardly from the wall to the screen-cleaning element and encircle the latter as shown in Fig. 1. These baflie plates 69 have a staggered relation with the plates or rings 68. The purpose of these rings 68 and baille plates 69 is to compel all the pulp to be forced back and forth through the screen a plurality of times 1 during its passage from the inlets to the outlet l5, 5, and to prevent the possibility that any of the pulp will flow downwardly along the inner face of the wall of the casing to the tailings outeach blade having its width dimension inclined backwardly relative to the screen and having the portion ofits trailing sid adjacent the screen concavely curved whereby the movement of the blade relative to the screen produces a waste-- removing suction at the concavely curved portion of the trailing side which removes from the screen any waste matter accumulating thereon.

2. A pulp-screening machine comprising a casing having an intake and a screened pulp out- 4 let, a cylindrical screen within the casing, means within the screen to pulsate the pulp back and forth through the screen as it flows from the intake to the outlet, a screen-cleaning member encircling the screen, means to rotate said member about the screen, baflie plates carried by the rotating screen-cleaning member and extending circumferentially thereof, and other baffle plates carried by the wall of th casing and extending radially inwardly therefrom and cooperating with the baflle plates on the screen cleaning element to cause the pulp flowing between the screen and the casing to have a sinuous course.

3. A pulp-screening machine comprising a casing having an intak and a screened pulp outlet, a cylindrical screen within the casing, means to pulsate the pulp back and forth through the screen as it flows from the intake to the outlet,

a screen-cleaning member encircling the screen and provided with baflle plates, and other baffle plates exterior to the screen-cleaning member and carried by the wall of the casing, said other baiiie plates extending inwardly from said wall and having their inner edges situated closely adjacent the screen-cleaning element, the baffle plates on the screen-cleaning element and those on the casing having a staggered arrangement.

4. A pulp screen comprising a casing having a pulp inlet and a screened-pulp outlet, a screen between the inlet and the outlet, a screen-cleaning member having a plurality of blades on the inlet side of the screen closely adjacentthereto, and means to move the blades relatively to the screen in a path parallel thereto, each blade having its width dimension inclined backwardly relative to the screen and the direction of movement of the blades, the outer or leading side of each blade being convexly curved from one edge to the other and the trailing side of each blade being concavely curved at the inner portion thereof which is nearest the screen and convexly curved at the outer portion thereof, whereby the flow of pulp over the blade as the latter-is moved relative to the screen produces a waste-removing suction between the concavely curved portion of the trailingside of the blade and the screen sufllcient to withdraw from the screen any waste matter that has accumulated thereon.

NELSON M. KNIGHT. 

